For many years people have been trying to create better stereoscopic 3D displays, and this invention provides a further advance in this field.
A stereoscopic display gives the illusion of depth in the image by giving each eye a different perspective of a scene, as would happen in reality. The brain then fuses these perspectives together to form a 3D representation of the image in the brain. For example, this may be done by displaying one perspective with one polarization, and the other perspective in a different polarization. A viewer can then see stereoscopic depth by wearing glasses where each eye piece only allows the appropriate polarization to pass.
An auto-stereoscopic display is a display that gives stereoscopic depth without the user needing to wear glasses. It does this by projecting a different image to each eye. These displays can be achieved by using parallax optic technology such as a parallax barrier or lenticular lenses.
These types of displays are well known in the literature. For instance, the design and operation of a parallax barrier for 3D is well described in a paper from the University of Tokushima Japan (Optimum parameters and viewing areas of stereoscopic full colour LED display using parallax barrier, Hirotsugu Yamamoto et al., IEICE trans electron, vol E83-c no 10 October 2000).
In summary, FIGS. 1(a) and 1(b) show the basics of the parallax barrier operation and design.
They show a cross sectional diagram of an auto-stereoscopic parallax barrier design. The images for the left and right eye are interlaced on alternate columns of pixels, as for previous designs.
The slits in the parallax barrier allow the viewer to see only left image pixels from the position of their left eye, right image pixels from the right eye.
The viewer may look on axis at the display to see a stereoscopic view, but note that they may also see a stereoscopic view off axis as shown in FIG. 1b, the dotted lines. The on axis view is termed the primary viewing window, and the off axis view is called the secondary viewing window.
The same 3D effect can be achieved by using lenticular lenses. Each lens is substantially equivalent to a slit on the parallax barrier. FIGS. 2(a) and 2(b) show a conventional 3D system using lenticular lenses.
The lenses image the pixels to the viewer (who is typically 300 mm from the panel). As shown in the diagram, light from the left pixels is directed into the observers left eye, and vice versa. To achieve this the focal length is typically set such that it is about equal to the lens-pixel separation distance, (so that the focal length of the lens is approximately at the plane of the pixels).
The lenticular lenses may also have a light blocking material between the lenses as is known from GB patent application 0320358.5 giving advantages including reduced light leakage between the lenses.
In many cases autostereoscopic 3D displays are needed that can also be switched into regular 2D displays. This can be achieved by using a liquid crystal parallax barrier. The switchable parallax barriers have the disadvantage that they are inefficient in 3D mode (reducing transmission by −65%). This is a major disadvantage if the display is mostly used as a 3D display such as for a 3D camera. In addition the 3D quality is not optimal.
Switchable microlenses are well known and are described in the paper, Commander et al, EOS Topical Digest Meetings, Microlens Arrays, vol 5 (1995), pp72-76.
Philips invented a system (U.S. Pat. No. 6,069,650) that uses switchable lenses in combination with a liquid crystal display (LCD) to create the 3D effect. These are efficient in both 2D and 3D modes, and use a liquid crystal to either index match or index mismatch lenses embossed in a plastic sheet.
The Philips system has advantages that the 3D mode is more efficient than parallax barrier systems and the 3D quality can be higher. It also has disadvantages that the system is more complicated to manufacture, and it may be very difficult to match the refractive index of the lens structure with the refractive index of the liquid crystal (LC) exactly. This is partly because the index of the LC can vary with wavelength and temperature. Any slight mismatch of the LC and lens structure causes slight residual lensing effect, any residual lensing effect will degrade the uniformity of the 2D mode.
Another Philips system described in WO05101855A1, uses micro-electro-wetting lenses that can be built into a stereoscopic 3D display allowing switching between 2D and 3D modes. The manufacture of these systems is complicated.
Another Philips system described in US2007/0296911A1, uses graded refractive index lenses (GRIN lenses) that can be built into a stereoscopic 3D display allowing switching between 2D and 3D modes. It is difficult to control the refractive index profile of the lens precisely enough to create a high quality 3D mode. This can be especially true of the regions between the lenticular lenses.
WO 2010/150166 and US 2008/0013002 (Philips) propose system using switchable lenses in combination with a liquid crystal display (LCD) that are generally similar to the system of U.S. Pat. No. 6,069,650.
US 2007/0018585 proposes a multiple view display, for example for use in a car. A switchable diffuser (such as a PDLC) is placed between a lenticular array and an electro-optic layer. A multiple view mode may be obtained by controlling the diffuser to be transparent, and a single-view mode may be obtained by switching the diffuser so that it diffuses the light produced by a backlight so that sub pixels are uniformly illuminated.
US 2010/0026920 proposes a component having a liquid crystal layer with an overlaying lens array. A GRIN lens array may be defined in the liquid crystal layer, so that the overall optical effect is given by the sum of the lensing effect of the GRIN lens array in the liquid crystal layer and the lensing effect of the overlying lens array. To obtain a 2-D image, the GRIN lens array in the liquid crystal layer may be arranged to cancel the effect of the overlaying lens array.
U.S. Pat. No. 6,246,451 proposes a lens array 4 with a “light directivity control element” based after the lens array. The light directivity control element has spaced-apart stripes of PDLC provided between substrates. The stripes can be driven to be either transmitting or scattering, whereas regions of the light directivity control element between the PDLC stripes remain transmissive. A 2-D mode, or a directional mode, can be obtained by causing the PDLC regions to be scattering or transmissive respectively
US 2003/0063186 proposes defining a lens array in a liquid crystal layer by applying a voltage that varies with the position across the liquid crystal layer, so as to induce refractive index variations across the liquid crystal layer. If no voltage, or a uniform voltage, is applied, the liquid crystal layer has a uniform alignment and a uniform refractive index—so, in the 2D mode there is no lens array.
As such there is no known solution which enables a high quality microlense 2D/3D switchable display that is entirely satisfactory.